This invention relates to a process and apparatus for controlling the amount of warp size composition added to the threads on a running warp sizing apparatus.
Warp sizing is used to protect warp threads and prevent abrasion during the weaving process in textile manufacturing. Warp sizing consists of a coating, typically of starch or a polyvinyl alcohol-based composition, which is applied prior to weaving by running a "sheet" of threads through a size solution, followed by drying. The machine used to accomplish this is known in the art as a "slasher." Accurate and precise application of size solids is important for consistent high weaving efficiencies and for optimum economy. New high-speed looms, incorporating projectiles, rapiers, or air jets, have significantly narrowed the limits of size add-on for efficient performance. (Add-on is defined as the weight of warp size solids deposited on the yarn relative to the weight of the dry, unsized yarn, and is normally expressed as a percent). Traditionally, the textile industry has used more sizing than was required, to ensure that sufficient sizing was used. However, this is no longer practical, since oversizing as well as undersizing can have severely detrimental effects on weaving performance in modern looms. Oversizing can result in excessive shedding of excess size, which flakes off of the fibers due to abrasion. This excess size can cause buildup in the weaving looms, causing defects in the woven cloth and process interruptions. Oversizing can also result in excess tension in the loom. Undersizing results in weak warp yarns which may fail under the stresses applied in the loom. Undersizing also results in "hairy" yarn which interferes with the travel of the filling yarn across the warp, thus resulting in weaving defects, particularly when air jet looms are used. The present invention permits simple, accurate, and automatic control of size add-on.
Adjustment of the amount of size on textile warp yarns by manipulating pressure on the nip rolls in size boxes has been known for some time. However, all the known references involve controlling nip roll. spacing, either alone or in combination with the sheet speed, on the basis of a measured variable which is related only indirectly to the amount of size add-on. None measures deposited size solids directly.
U.S. Pat. No. 3,253,315, Eiken, discloses an apparatus for measuring the electrical resistance of the warp sheets emerging from a size box, and adjusting this parameter to a preset value by adjusting the spacing of the squeeze rollers. This adjustment can be used in combination with means for controlling the speed of advancement of the sheet so that a given quantity of sizing will be obtained on the sheet for a particular constant pressure applied to the sheet by the squeezing rollers.
Another method which has been used is measurement of the amount of size consumed over a given interval using a flowmeter. The integrated reading is compared to a set point whose value is determined by calculation from an assumed rate of liquid pick-up for the particular yarn and the formulated level of solids in the size solution.
Japanese document No. 59-187662-A, Nisshin Spinning, discloses use of an electric signal representing the viscosity of the size to control spacing of the rollers to maintain a constant level of the liquid picked up by the sheet. The signal is sent to a programmable control unit to provide an output signal which is converted into air pressure, which pressurizes the squeeze rollers so that sizing is controlled. The electrical signal representing viscosity is combined with a second electrical signal representing speed, and a third reference signal. These signals are fed into a specially programmed computer whose output signal is converted to an electropneumatic converter to give a pneumatic pressure according to the monitored conditions Measurement of viscosity itself is accomplished by intermittently filling a calibrated orifice cup to a given level and the measuring the time it takes to empty through the orifice.
Japanese document No. 73-01473-R, as reported in Derwent Abstract 17279U-F, discloses control of the amount of size by dielectric measurement of "sheet moisture regain."
In spite of these efforts, there has been no reported method or apparatus for direct on-line measurement of the "add-on", or amount of dry warp size material added to the threads of a warp sizing apparatus (slasher) or use of such a measurement to adjust the amount of add-on to the desired level.